Mechanisms for Radiation Damage to DNA: LET Effects

DNA 辐射损伤机制：LET 效应

• 批准号: 8819515
• 负责人: MICHAEL Douglas SEVILLA
• 金额: $ 20.37万
• 依托单位: OAKLAND UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-07-01 至 2016-02-29
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8819515
• 关键词: Address; Base Sequence; Biological; Biomedical Research; Cations; Chemicals; Complement 5a; Complex; Cyclotrons; DNA; DNA Damage; DNA Structure; Dependence; Deposition; Development; Electron Spin Resonance Spectroscopy; Electron Transport; Event; Free Radicals; Genetic Recombination; Goals; Health; Heavy Ions; High Pressure Liquid Chromatography; Ions; Kinetics; Laboratories; Lead; Linear Energy Transfer; Magnetic Resonance; Magnetic Resonance Spectroscopy; Modeling; Molecular; Monitor; Oxidation-Reduction; Process; Property; Psychological Techniques; Radiation; Radiation Induced DNA Damage; Reaction; Research; Running; Secondary to; Site; Spatial Distribution; Sugar Phosphates; Techniques; Temperature; Testing; Theoretical model; Thermodynamics; Time; Vertebral column; Work; base; complement C3 precursor; density; ds-DNA; electron energy; inorganic phosphate; insight; ionization; irradiation; oxidation; phosphorothioate; radiation effect; sugar; theories

DESCRIPTION (provided by applicant): Our laboratory continues the development of a comprehensive model of DNA radiation induced to damage, one that describes physicochemical events from the initial track structure and DNA ion-radical-excited state formation through hole and electron transfer, to chemical events involving free radical processes that lead to secondary radicals and, finally, to combination and redox processes that result in DNA damage such as base and sugar damage, strand scission and associated base release. The spatial distribution of the damage sites is a critical portion of our model as it determines the biological effectivenes of the radiation damage. The overall goal of the current proposed effort is to test several aspects this overall model, to modify it as appropriate and thereby elucidate fundamental mechanisms of radiation damage to DNA by radiations of varying linear energy transfer (LET). These studies will be performed under conditions that emphasize the direct effect of radiation, and will employ magnetic resonance spectroscopies (ESR), product analyses, gamma and cyclotron heavy ion-beam irradiation, as well as theoretical modeling including time dependent density functional theory (TD- DFT). The first aim will test the hypotheses that the mechanism of hole transfer process from the sugar- phosphate backbone to the DNA bases is base sequence and temperature dependent. Oligomer sequences chosen for study will provide the sequence dependence and temperature dependence of the mechanism of long range hole transfer from the DNA backbone through A runs to a remote G in DNA. The second aim will test the hypothesis that the yields of two strand break radicals, at C5' and C3' sites in the DNA sugar phosphate backbone are LET dependent and are produced by specific oxidative and reductive mechanisms, respectively. We will test the hypothesis that, as LET increases, spatial clustering of these radicals increases to form multiple proximate strand breaks (multiple damage sites); however, the highest yields of sugar radicals do not occur precisely at the Bragg peak of the ion beam path. This would suggest that ion and radical recombinations inhibits cluster formation at the track ends. The third aim will employ theoretical calculations to further test and confirm molecular mechanisms proposed in each of the aims. Especially significant will be the use of DFT theory to accurately predict core-excited states and test the hypotheses that one low energy electron can induce a double strand break and further that double oxidation of sugar sites leads to strand breaks without radical involvement. We believe these efforts will allow us to establish new insights into fundamental radiation processes important for biomedical research.

描述（由申请人提供）：我们的实验室继续开发DNA辐射诱导损伤的综合模型，该模型描述了从最初的轨道结构和DNA离子自由基激发态通过空穴和电子转移形成的物理化学事件，到涉及自由基过程的化学事件，导致二次自由基，最后，结合和氧化还原过程导致DNA损伤，如碱基和糖损伤，链断裂和相关的碱基释放。损伤地点的空间分布是我们模型的一个关键部分，因为它决定了辐射损伤的生物效应。目前提出的努力的总体目标是测试这个整体模型的几个方面，适当地修改它，从而阐明通过不同线性能量转移（LET）的辐射对DNA的辐射损伤的基本机制。这些研究将在强调辐射直接影响的条件下进行，并将采用磁共振波谱（ESR）、产品分析、伽玛和回旋重离子束辐照，以及包括时间相关密度泛函数理论（TD- DFT）在内的理论建模。第一个目的将检验从糖-磷酸主链到DNA碱基的空穴转移过程的机制是碱基序列和温度依赖的假设。所选择的寡聚体序列将提供DNA主干通过A链到远端G的远程空穴转移机制的序列依赖性和温度依赖性。第二个目标将测试DNA糖磷酸主链中C5‘和C3’位点的两条链断裂自由基的产率是LET依赖的，分别由特定的氧化和还原机制产生。我们将测试假设，随着LET的增加，这些自由基的空间聚集增加，形成多个近链断裂（多个损伤位点）；然而，糖自由基的最高产率并不恰好发生在离子束路径的布拉格峰。这表明离子和自由基的重组抑制了轨道末端的团簇形成。第三个目标将采用理论计算来进一步测试和确认每个目标中提出的分子机制。特别重要的是使用DFT理论来准确预测核心激发态，并验证一个低能电子可以诱导双链断裂的假设，进一步证明糖位点的双重氧化导致链断裂而不涉及自由基。我们相信这些努力将使我们能够